This invention relates to a calibration pattern display system for use with a color display characteristic measurement apparatus which picks up an image of a specified measurement image displayed on a color display apparatus such as a color CRT (Cathode Ray Tube) and measures a display characteristic such as a geometric image distortion or a convergence using the picked image, and also to a display characteristic measurement apparatus for a color display apparatus to which the calibration pattern display system is applicable.
Conventionally, there has been known a display characteristic measurement apparatus for measuring a display characteristic such as a convergence of a color display apparatus such as a color CRT, a color LCD (Liquid Crystal Display) or a color PDP (Plasma Display Panel). This display characteristic measurement apparatus includes a color image pickup unit for picking up an image of a specified measurement pattern color-displayed on a color display apparatus to be measured while separating this image into images of respective color components of R (red), G (green) and B (blue), an image processor for conducting a predetermined measurement after processing the images of the respective color components, and a display device for displaying a measurement result.
The display characteristic measurement apparatus calculates a luminous position of a measurement pattern on a display surface of a color CRT to be measured based on a focal point of the measurement pattern on a sensing surface of an image pickup unit and a relative positional relationship between the image pickup unit and the color CRT using the picked image of the measurement pattern, and further calculates the degree of geometric image distortion and a misconvergence amount using the calculation result.
For example, a convergence measurement apparatus operates as disclosed in Japanese Unexamined Patent Publication No. 8-307908. The apparatus picks up an image of a specified white measurement pattern displayed on a color CRT to be measured using a camera provided with a color area sensor such as CCDs. During the image processing, the apparatus calculates a focal point of a measurement point of the measurement pattern on a sensing surface of the color area sensor for every picked image of each color component R, G, B, and calculates a display position of the measurement point of the measurement pattern on a display surface of the color CRT based on the calculation result and the relative position of the camera with respect to the color CRT. The apparatus displays a relative displacement of the display positions of these measurement points.
As described above, the display characteristic measurement apparatus converts the focal point of the measurement point of the measurement pattern on the sensing surface of the image pickup unit into the display position of the measurement position on the display surface of the color CRT to be measured. Accordingly, operation parameters including a displacement of the area sensor with respect to an optical axis, a focal length of a taking lens and a magnification largely influence the above conversion.
Thus, the display characteristic measurement apparatus is calibrated without fail before conducting measurement using a special calibration chart as shown in FIG. 11. FIG. 11 shows a conventional display characteristic measurement apparatus 100. An image of a chart 103 (chart on which a black crosshatched pattern 105 is drawn on an opaque white board) for calibration illuminated by a fluorescent lamp 104 is picked up by an image pickup unit 101 of the display characteristic measurement apparatus 100. The operation parameters in the processing for converting the focal point into the display position using the picked image are determined by an apparatus main body 102.
Since the calibration chart 103 is illuminated by the fluorescent lamp 104 having a luminescence characteristic different from that of the color CRT to be measured in the calibration for the conventional display characteristic measurement apparatus, the operation parameters determined in the calibration do not precisely agree with the operation parameters of the measuring system. This causes a reduction in the measurement accuracy.
Particularly, in the convergence measurement, parameters including, e.g., a focal length of the image pickup unit 101 and a distortion need to be determined according to the luminescence characteristic of the respective color components R, G, B of the color CRT to be measured. However, since the calibration chart 103 is illuminated by a fluorescent white light, it is difficult to precisely determine the operation parameters and there is a specified limit in improving the measurement accuracy.
It is an object of the present invention to provide a calibration pattern display system, a system and method for calibrating a display characteristic measurement apparatus which have overcome the problems residing in the prior art.
According to an aspect of the present invention, a calibration pattern display system for displaying a calibration pattern to be used for calibrating a display characteristic measurement apparatus for measuring a display characteristic of a display apparatus, the calibration pattern display system comprises a display unit which displays a calibration pattern at substantially the same luminescence characteristic as that of a display apparatus to be measured.
According to another aspect of the present invention, a calibration system for calibrating a display characteristic measurement apparatus for measuring a display characteristic of a display apparatus, the calibration system comprises: a calibration pattern display unit which displays a calibration pattern at substantially the same luminescence characteristic as that of a display apparatus to be measured; an image pickup unit which is provided in a display characteristic measurement apparatus, and picks up a calibration pattern displayed on the display apparatus to generate image data; and a calculator which calculates, based on the image data generated by the image pickup unit, calibration data for the display characteristic measurement apparatus.
According to still another aspect of the present invention, a method for calibrating a display characteristic measurement apparatus for measuring a display characteristic of a display apparatus, the method comprises the steps of: displaying a calibration pattern at substantially the same luminescence characteristic as that of a display apparatus to be measured; picking up a displayed calibration pattern by an image pickup unit of a display characteristic measurement apparatus to be calibrated, and generating image data corresponding to the displayed calibration pattern; calculating, based on the generated image data, a focusing position of the calibration pattern on an image sensing surface of the image pickup unit; and setting, based on a display position of the calibration pattern and a calculated focusing position, an operation parameter for calculating a display characteristic of a display apparatus.